Pointing Pair
Prerequisites: Hidden Single
Overview
When a candidate in a box is restricted to a single row or column, it can be eliminated from that row or column outside the box.
How It Works
A pointing pair occurs when a digit's candidates within a box all lie in the same row (or column). Since the digit must appear in one of those cells, it cannot appear anywhere else in that row (or column) outside the box.
When To Use It
Look for pointing pairs after filling in all obvious singles. They are one of the first intermediate techniques you should learn.
How To Detect It
For each box, check each missing digit. If all candidates for that digit fall in a single row or column, you have a pointing pair (or triple). Eliminate that digit from the rest of the row or column.
Visual Example
Step 1 of 7
Box-Line Interaction
A Pointing Pair arises when two constraint systems — a box and a line (row or column) — overlap. If a digit's candidates within a box all fall on the same line, those candidates 'point' along that line and eliminate the digit from the rest of it.
Practice
A Pointing Pair lets you eliminate along a line. Use it, then fill the Naked Single that results.